Sensitization of TRPV1 by PAR activation. A - D. Heat-activated currents were significantly enhanced in c. 10% of neurons by application of PAR1-AP and PAR4-AP. Single traces in panels to left are taken from time courses shown in right hand panels. Both PAR1-AP (TFLLR at 100 μM) and PAR4-AP (AYPGKF, 200 μM) caused long-lasting sensitisation. Sensitization showed complete tachyphylaxis on a second application.
E. Percentage sensitization in experiments similar to those in A. Thrombin (100 nM), trypsin (100 nM), PAR1-AP and PAR4-AP all caused approximately a doubling of the inward current elicited by heat. Thrombin-induced sensitisation was largely blocked by the PKC inhibitor Ro318220 (1 μM) and by the broad-spectrum kinase inhibitor staurosporine (1 μM, both applied throughout the experiment).
F, G Calcium imaging experiments to monitor functional sensitization of TRPV1 by thrombin. F shows typical experiment in which increases in [Ca]i elicited by successive brief exposures to capsaicin (500 nM, 1 s) were enhanced by exposure to thrombin (100 nM, black bar). All experiments performed in adult mouse neurones. G shows percentage of cells sensitized in experiments similar to those shown in F on neurons from WT and PAR1-/- adult mice. Difference was significant (χ2 test, *, p < 0.05).